This invention pertains to a process for the oxidation of aliphatic hydrocarbons, such as alkanes and monoolefins, to products comprising more highly unsaturated aliphatic hydrocarbons. More specifically, this invention pertains to the oxidation of butane to butadiene.
Unsaturated aliphatic hydrocarbons, such as monoolefins and diolefins, are useful as monomers and comonomers in the preparation of polyolefin plastics.
U.S. Pat. No. 3,180,903 discloses a process for the dehydrogenation of aliphatic hydrocarbons containing from two to five carbon atoms. Butanes, for example, can be converted to butenes and butadienes. The catalyst used in this process is taught to contain chromium oxides or molybdenum oxides supported on a gel-type alumina. Optionally, the catalyst may contain one or more alkali metal oxides. Disadvantageously this process is limited to a low hydrocarbon conversion and a low ultimate yield of butadiene.
U.S. Pat. No. 3,119,111 discloses a process for the oxidative dehydrogenation of a C.sub.4 to C.sub.6 alkane having a four carbon chain to a 1,3-alkadiene. The reaction occurs in the presence of oxygen and a catalyst containing an alkali metal molybdate, such as lithium molybdate. Disadvantageously, this process requires potentially explosive mixtures of alkanes and oxygen.
U.S. Pat. No. 3,862,256 discloses a process for the oxidative dehydrogenation of paraffin hydrocarbons, such as butane, over a catalyst containing oxy compounds of molybdenum and magnesium, and optionally, vanadium. When butane is contacted with the catalyst, the products include butenes and butadiene: however, the selectivity and space-time yield of butadiene is lower than desired.
U.S. Pat. No. 4,229,604 discloses a process for the oxidative dehydrogenation of a paraffin, such as butane, to unsaturated hydrocarbons, such as butenes and butadiene. The catalyst is an oxide of molybdenum deposited on a carrier. The carrier is selected from the group consisting of granulated porous crystalline silica modified with magnesia, magnesium-titanium oxides, or magnesium-aluminum oxides. It is taught that the silica carrier is prepared from an an alkali metal silicate. It is further taught that on the surface of the catalyst there exists an active magnesium molybdate. Disadvantageously, the catalyst of this process produces a selectivity and space-time yield of butadiene which is too low for industrial use.
While the oxidation of aliphatic hydrocarbons is well researched in the prior art, the selectivity and productivity to particular unsaturated hydrocarbons, such as diolefins, fall short of those which are desired for commercial exploitation. Accordingly, it would be desirable to have a selective, direct oxidation of an aliphatic hydrocarbon, such as an alkane or monoolefin, to the corresponding unsaturated aliphatic hydrocarbons, specifically the diolefin. It would be more desirable if the alkane is butane and the diolefin is butadiene. It would be most desirable if such an oxidation produced a high selectivity and space-time yield of the diolefin and other olefins, and correspondingly low selectivities to deep oxidation products, such as carbon dioxide.